1. Technical Field
The entire disclosure of Japanese Patent Application Nos: 2006-262537, filed Sep. 27, 2006 and 2006-262538, filed Sep. 27, 2006 and 2006-262649, filed Sep. 27, 2006 and 2007-178252, filed Jul. 6, 2007 are expressly incorporated by reference herein.
The present invention relates to an image development apparatus using a liquid toner being a result of dispersing toner particles in a carrier solution, an image forming apparatus using the image development apparatus, an image development method, and an image forming method using the image development method.
2. Related Art
A previous image forming method using a liquid toner is described in Patent Document 1 (JP-A-2002-278291). Patent Document 1 describes an image forming method of using a developing roller carrying thereon a liquid toner for latent image development on a photosensitive element. In the method, a compression roller is used for compressing the liquid toner on the developing roller before image development, and a voltage is applied to both the developing roller and the compression roller in such a manner that the application voltage for the compression roller is higher than that for the developing roller. Such voltage application prevents any possible image fogging and inconsistencies in density so that the resulting images can be of high quality.
In an image forming apparatus, a toner layer on a developing roller is compressed and then is made like a film. This eases the movement of the toner layer in the later image developing and transferring so that the resulting images can be free from disturbance with high efficiency of image developing and transferring.
Considered here is a case where such an image forming apparatus uses a printing method of using a liquid developer, in which toner particles each at least made of a coloring agent and a resin are dispersed by a dispersant in a nonvolatile carrier solution. Such a printing method may possibly cause various types of changes to the developer in terms of characteristics, i.e., conductivity, electric-charge characteristics, size distribution of toner particles, mobility of toner particles, and others. The change of conductivity in the developer is caused due to any change observed in the developer over long-time running of an image forming apparatus, and any change occurred to the moisture content in the carrier solution as a result of moisture absorption due to the influence of temperature and humidity environment. The possible cause of the change of electric-charge characteristics is any change of moisture content, or any change observed in the condition of adhesion of a dispersant to toner particles as a result of any over-time change and temperature change. The change of size distribution of toner particles is caused by agglomeration of the toner particles, which is possibly caused by any change observed in a dispersant in terms of the condition of adhesion. The change of mobility of toner particles observed with respect to an electric field occurs as a result of these changes described above.
If with an image forming apparatus that collects, for recycle use, any developer not used for development to a photosensitive element as is transferred to a non-image portion of a developer carrier, some changes may be observed in a dispersant in terms of adhesion to the toner particles, i.e., the amount of dispersant to be adhered to the toner particles may be changed. This is because, in such an image forming apparatus, a developer to be reused for recycling purpose is the one having been passed through an electric field in the nip of a compression member formed with a developer carrier, i.e., compression member nip, and an electric field in the nip formed by the developer carrier and a photosensitive element, i.e., developer nip. Therefore, the toner particles are pushed against the developer carrier by the electric field of the compression member or that of the developer nip, i.e., non-image portion. As a result, the toner particles are pushed against one another, and this deteriorates the dispersion among the toner particles. The particles are thus agglomerated and are applied with an electric field so that the dispersant possibly falls off from the toner particles. This is the reason of the possible change in the dispersant in terms of adhesion to the toner particles, i.e., the amount change of the dispersant to be adhered to the toner particles. Moreover, in the developer nip, in an image portion, the toner particles are mostly subjected to development to a photosensitive element together with a carrier solution, and the carrier solution is partially left on the developer carrier. On the other hand, in a non-image portion, the tone particles are mostly remained on the developer carrier together with the carrier solution, and the carrier solution is partially transferred to the photosensitive element. As such, in the developer carrier after image development, a ratio between the toner particles and the carrier solution varies depending on the density of a printing image. With solid printing, for example, any developer showing a considerably high ratio for the carrier solution is remained on the developer carrier, and this developer is collected by a cleaner. As such, the liquid to be collected by a cleaner for recycling purpose has such a ratio different from that of the original developer, and unless otherwise adjusted, the developer is reused with a different ratio. Even if the developer is adjusted in ratio, depending on the adjustment accuracy, the resulting developer to be reused does not always have exactly the same ratio as that of the original developer. As a result, the developer may suffer from some changes of ratio between the toner particles and the carrier solution.
Such changes observed in a developer affect the behaviors of particles therein in a process of moving the particles by electric fields of a compression member nip, a developer nip, a transfer nip, and others. This resultantly causes problems of causing a change of image density, image disturbance in streaks called ribs, fogging over a non-image portion, and others.